Demand for improved fuel economy has compelled motor vehicle manufacturers to increase engine efficiency and reduce weight of their vehicles. Replacing metal, where possible, with lighter materials, such as plastics and composites, has contributed to lighter vehicles with resultant increases in fuel economy. For example, hoods for the engine compartments of large trucks are now most often made from substantially non-metallic materials, such as fiberglass or plastics.
Engine efficiency and emissions are substantially reduced by increasing the operating temperature of the engine. A coolant system comprising a liquid coolant flowing through an engine and a radiator is most commonly used to regulate engine temperature. This system does little to reduce heat transfer from the engine to a hood so, as the engine's operating temperature increases, the hood temperature also increases. At such elevated temperatures, engine life is reduced and non-metallic hood materials tend to warp or degrade, which can lead to safety and aesthetic concerns.
Prior art has attempted to remove heat from an engine compartment using openings to the outside. Such openings include vents or ducts. The various air openings of prior art permit airflow both into and out of the engine compartment, and do not restrict flow to a particular direction. This can decrease cooling efficiency at low speeds by pulling air through the openings in a reverse direction so that cooling air can by-pass the radiator.
U.S. Pat. No. 6,302,228 to Cottereau et al. teaches at least one continuous duct located between the hood and the engine. The duct includes a forward inlet positioned at the front of the vehicle for receiving air, at least one aspirator inlet, and an outlet for directing the air from duct. The aspirator inlet opens into the engine compartment. The velocity of the air in the duct, and correspondingly reduced pressure, relative to the hot air in the engine compartment sucks the hot air into the duct. In this manner, the temperature of the engine compartment may be reduced thereby reducing the operating temperature of the engine. Unfortunately, Cottereau requires a complex duct system integrated with the hood of a vehicle. This adds considerable to cost and also adds undesirable weight to the hood.
U.S. Pat. No. 6,230,832 to Mayenburg et al. teaches an underhood airflow management system. The system permits air to entire the engine compartment at the forward end of the compartment. Air flows past the engine and exits at cowl openings at the rear of the engine compartment. The cowl openings are substantially vertical slits. Preferably, the compartment is sealed to prevent air from escaping before passing over the engine. In operation, the cowls do not positively draw air from the compartment.
Prior art also teaches engine compartment hoods having vents that provide air for combustion. U.S. Pat. No. 5,042,603 to Olson teaches a modified NACA duct for the air intake of an internal combustion engine. In the field of aeronautics, the National Advisory Council on Aeronautics has defined air intake ducts of a specific configuration as NACA ducts. Such ducts include a narrow and shallow leading edge and a wider and deeper trailing edge having a port for air intake. Olson teaches a NACA duct having a cover plate and base member for removing surface water from the engine's air intake stream. Olson does not use the duct to cool the engine compartment. Other vented hoods for engine air intake do not use NACA ducts. For example, U.S. Pat. No. 5,618,323 to Shearn describes a combustion air intake comprising a duct and a chamber for deceleration of the airflow. The chamber is adapted to remove moisture from the airflow. U.S. Pat. No. 4,971,172 teaches an air duct comprising several bends, whereby liquid water is prevented from reaching the engine air intake.
Assemblies are known for supplying cooling air to an internal combustion engine, particularly engines which are air-cooled only. Such engines often include cooling fins and cowlings surrounding the engines that direct air over the fins. Directing means includes vents, ducts, scoops and the like. With air-cooled engines, constant airflow is essential to avoid overheating, especially at idle. Heat transfer considerations make air-cooling impractical for large engines. Further, difficulties in maintaining constant operating temperatures make air-cooled engines less efficient than their liquid-cooled counterparts.
New emission standards and higher operating temperatures require a cooling system that reduces the temperature of an engine compartment of a liquid-cooled internal combustion engine. Benefits would include improved engine life and reduced temperature of a surrounding cowling or hood. Prior art has resorted to complex ducting systems or, relatively ineffective, simple forced air vents. In no case is airflow mechanically restricted to a single direction. Further, prior art openings often divert air around the radiator, thereby decreasing cooling efficiency of a radiator at idle